Electric arc device



Filed March 30, 1940 (Ittorneg Patented Nov. 10, 1942 ELEOTRIC ARCDEVICE James R. Alburger, Merion, Pa., assignor to Radio Corporation ofAmerica,

Delaware a corporation of Application March 30, 1940, Serial No. 326,833

6 Claims.

This invention relates to mercury vapor lamps, rectifiers and likeelectric are devices of the type requiring the use of an auxiliaryelectrode for lighting or starting the arc.

It has previously been proposed to employ a bimetallic element or stripas a movable support for a starting electrode in a mercury arc device.The bimetallic element in such cases is arranged to be deformed when aheating current is passed through it and the mercury anode in which itis immersed when the device is unenergized. The heating current servesto vaporize some of the mercury and, as the starting electrode is movedby the bimetallic element through this conductive vapor, an arc isstarted which, when extended and transferred to the main cathode, lightsup or otherwise starts the device. Since the vaporized mercury comprisesa conductive medium which permeates the interior of the envelope, it isapparent that the heating-current may continue to flow through thedevice even when the bimetallic element operates, by its deformation, towithdraw the starting electrode from the liquid mercury.

The heating current in devices of the general character described isusefully employed only during the starting period. If the heatingcurrent continues to flow during the normal operating periods, it mayadversely affect both the operating characteristics and the life of thedevice. It is, therefore, usual to employ an extemal relay in theheating circuit between the heating current source and the auxiliaryelectrode lead of the tube and to open this relay either manually orautomatically when the arc has been started.

Even where the use of the heretofore necessary separate electrodeterminal (for the starting electrode), auxiliary heating circuit, andauxiliary relay can be tolterated, their use fails to afford asatisfactory solution of the problem principally because in the tubes ofthe prior art the practice has been to so dispose the starting electrodethat it remains in the path of the main arc irrespective of whether ornot it is connected to the heating circuit. This results in excessiveheating of the bimetallic element upon which the starting electrode issupported and in any event augments the tendency of the mercury to forman amalgam with the nickel and other thermal responsive metals of whichthe bimetallic element is constituted.

Accordingly, the principal object of the present invention is to obviatethe above-described and other less apparent objections to electric arcdevices of the general character described.

Another and related object of the invention is to provide a reliable andflickerless mercury arc lamp and one characterized by its economy ofparts and absence of troublesome auxiliary starting apparatus.

Another and more specific object of the invention is to provide amercury vapor device wherein the starting electrode is movable out ofthe path of the are between the anode and cathode whereby the dangers ofdestructive heating of this electrode and its support are substantiallyobviated.

Other objects and advantages will be apparent and the invention itselfwill be best understood by reference to the following specification andto the accompanying drawing wherein,

Figure 1 is a longitudinal view in perspective of a mercury arc lampconstructed in accordance with the principle of the invention andshowing, schematically, one manner in which it may be energized, and

Figure 2 is a longitudinal sectional view of another embodiment of theinvention.

Referring now to the drawing, and particularly to the mercury arc lampshown in Fig. l; the lamp bulb comprises a hermetically sealed evacuatedtransparent envelope 1 and has a reentrant press 2 through which but twoconductors 3 and 4, which are preferably constituted of tungsten, aresealed. Lead 3 which is shown in the drawing as connected to thenegative terminal of the electric source, exemplified by the battery B,will occasionally hereinafter be referred to as the cathode lead, andthe lead 4, which is connected to the terminal of the said source, willbe designated the anode sad. The cathode lead of the device of Fig. 1comprises a rod-like element which terminates at a point 3b immediatelyabove (say, .25" above) the surface of a pool of mercury 5.

In the usual mercury arc device wherein the necessary electricalconnection to the mercury pool comprises a short-lead which extends fromthe bottom of the pool directly through the wall of the envelope, theare under normal operating conditions extends between the surface of themercury (anode) and the cathode electrode. An'

arc to the surface of an unbroken pool of mercury is relativelyunstable, probably because the temperature of they arc sets upturbulations in the pool which cause the arc to dance about and toflicker. This, of course, is especially objectionable in the case of alamp for use, by way of example, in ultraviolet sound recordingapparatus.

To obviate such flickering the anode lead 4 extends into the mercurypool 5 and is provided with a return bend portion 4a which terminates ata point 42) adjacent the surface of the mercury pool and in line withthe terminal of the cathode lead 3. With this arrangement, the main arcin the device is confined to the area of the surface of the poolimmediately surrounding the point or terminal 4b of the anode lead andis substantially free from flicker.

As previously set forth, the present invention contemplates the use ofan auxiliary or arc-starting electrode which is movable out of the pathwhich it starts between the main operating elements. To this end,referring still to Fig. 1, the starting electrode, here designated 6, ismounted on the free end of a bimetallic element or strip l which isfixed at its opposite end to a conductive supporting arm 3 which, inturn, is fixed as by a strap or weld 8 to the cathode lead 3. Inasmuchas the tube contains mercury, it is desirable to construct thebimetallic strip of material which will not appreciably amalgamate withmercury. Nickel and tungsten have proven satisfactory in the aboverespect and exhibit the necessary different coefiicients of linearexpansion. In one successfully operated device, excellent result wereobtained using a strip of nickel wide and 5 mils thick, and a tungsten10 mil drawn wire, spot welded along the middle of the nickel strip. Asindicated in Fig. 1 Where the tungsten Wire of the bimetallic elementextends beyond the nickel the extended part may itself comprise the arcstarting electrode 6, in which case its free end is bent over downwardlyso that, when the device is at room temperature, it contacts the surfaceof the mercury pool 5.

The length of the bimetallic strip should preferably be made long enoughto lift the tip of the starting electrode out of the mercury pool andmove it beyond the point or terminal of the cathode 3 so that, when thearc which is initiated between the starting electrode and the surface ofthe mercury pool is transferred to the main electrodes, the startingelectrode will be entirely out of the short path between the point ofthe cathode and the surface area of the mercury adjacent the point ofthe anode.

Another embodiment of the invention is shown in Fig 2 wherein the highlyevacuated transparent envelope is designated it, a pool of mercury ii,and the necessary external leads are designated i2 and i3, respectively.These leads l2 and l 3 terminate above the surface of the pool H ininwardly directed spaced apart points l'3a and i311, respectively. Toeach lead there is at tached, preferably on the side nearer the wall ofthe envelope, a bimetallic element I i, l5, respectively, which, likethe element 1 of the device of Fig. 1, may comprise a nickel strip andan elongated tungsten wire which extends beyond the nickel parts. Inthis case, the tungsten wires, which are designated l6 and H,respectively, are bent inwardly and touch each other, when the device isat room temperature, to provide a conductive path for the heatingcurrent which,.in this case, is supplied by an alternating currentsource indicated symbolically at 13. When the device is employed as alamp, the source may comprise a -25 volt generator. The passage ofcurrent through the continuous path comprising the bimetallic elementsand tungsten wires generates heat which serves to vaporize the mercuryand thereby create a conductive path between the spaced apart points ofthe main operating electrodes l2 and i3. At the same time, the heat thusgenerated deforms or bends the bimetallic elements it and i5 outwardlybeyond the terminals of the main operating electrodes [2 and 13.

Other modifications of the invention will suggest themselves to thoseskilled in the art. It is to be understood, therefore, that theforegoing should be interpreted as illustative and not in a limitingsense except as required by the prior art and by the spirit of theappended claims.

What is claimed is:

1. A gas-discharge device comprising a pair of spaced arc-maintainingelectrodes, an auxiliary arc-starting electrode mounted upon anelectrode of said pair, and means to move said startin electrode out ofthe path of the arc which it starts between said pair of arc-maintainingelectrodes without altering the spacing therebetween.

2. A mercury vapor device comprising an envelope containing a pool ofmercury, an electrode mounted above said pool for maintaining an arctherebetween, an auxiliary electrode for starting an are between saidfirst-mentioned electrode and the surface of said pool, and means forconcentrating said are adjacent the surface area of said pool which liesbeneath said first-mentioned electrode.

3. The invention as set forth in claim 2 and wherein said last-mentionedmeans comprises a rod-like element within said pool and which terminatesadjacent the surface of said pool in line with the terminal end of saidfirst-mentioned electrode.

4. A mercury vapor device comprising an envelope containing a pool ofmercury, an electrode having a terminal spaced from the surface of saidpool for maintaining an are between it and the surface of said mercury,an arc-starting auxiliary electrode having a terminal immersed in saidpool adjacent the area thereof beneath said firstmentioned electrode,and thermally actuated means for moving the terminal of said auxiliaryelectrode out of said pool to a point beyond the terminal of saidfirst-mentioned electrode.

5. A mercury vapor device comprising an envelope containing a pool ofmercury, an anode comprising a point projecting from said pool, acathode comprising a conductor'having a terminal spaced from the surfaceof said pool in line with said anode point, a bimetallic elementconnected only at one end to said cathode conductor and an auxiliaryarc-starting electrode fixed to the other end of said bimetallicelement, said auxiliary electrode having a terminal which contacts thesurface of said poocl of mercury when said bimetallic element is atrest.

6. A gas-discharge device comprising a pair of are maintainingelectrodes mounted in spaced relation within a hermetically sealedenvelope, a bimetallic element supported at one end by one of saidarc-maintaining electrodes and an auxiliary arc-starting electrode.fixed to the other end of said bimetallic element and adapted to bemoved by said bimetallic element out of the path of the are which itstarts between said arc-maintaining electrodes and without disturbingthe initial spacing between said pair of electrodes,

JAMES R. ALBURGER.

